Bladed turbomachine rotors wherein an annular sideplate is secured axially abutting the periphery of the disk in the vicinity of the blade root attachment are well known in the art. Typically such sideplates are secured by means of cooperating dogs and lugs extending radially from the respective sideplate and disk. During assembly, the disk and sideplate are oriented so as to allow the lugs and dogs to pass axially via circumferentially intermediate gaps, then indexed rotationally so as to juxtapose the dogs and lugs in an engaged, axially interfering position.
The engaged disk and sideplate are locked against rotation by means of at least one locking element comprising, in the prior art, a key which is inserted into one of the plurality of gaps formed intermediate adjacent engaged dogs and lugs. The key is itself held in position by a sheet metal retainer sandwiched between the engaged sideplate and disk and having an axially extending tongue portion which is bent around the key so as to trap the key axially in the formed gap. U.S. Pat. No. 4,669,959 issued to Kalogeros is illustrative of the prior art configuration.
As the antirotation function requires only one of such keys, and as it is desired to minimize the amount of weight at the disk periphery, typical engine assemblies as a rule use no more than two such keys for safely securing the sideplate and disk against relative rotation. The remaining unfilled gaps interact with the radially flowing cooling air originating adjacent the rotor axis and flowing outward past the airseal into the surrounding annular working fluid flow stream. In the prior art, the gaps in the assembled rotor and sideplate open both radially and axially, and the aerodynamic interaction between the unfilled gaps and cooling air stream results in a small but significant aerodynamic heating and overall efficiency loss for the rotor and hence the entire gas turbine engine.
The antirotation keys of the prior art also require significant attention during the manufacturing thereof so as to insure a secure fit within the formed gap. As the gap opens both radially and axially, the key must match closely with the remaining disk and sideplate structure so as to avoid becoming dislodged during engine operation.
What is required is a sideplate, disk, and key assembly which reduces the aerodynamic losses imposed by the unfilled gaps of the prior art.